Power converting mechanism

ABSTRACT

In the electric actuator of the present invention, the power converting mechanism is provided for converting the rotary power of the motor into linear power of the driven member, which needs no special component part. Therefore, in comparison with the prior art power converting mechanism, it is advantage in that the scale of speed reduction and the stroke can be freely determined, with remarkably reduced number of parts and in low cost. The electric actuator according to the present invention is also provided with the improved clutch device employing the engagement of the weight and the recessed portion for secure transmission of the rotary power of the motor, resulting in full utilization of the capacity of the motor in simplified structure.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a power converting mechanismin an electric actuator for converting rotary power into linear power,and more particularly, to a power converting mechanism in an automobiledoor lock device suitable for use when the rotary power of aremote-controlled motor is converted into linear power of a part to bedriven (output member), thereby to automatically drive a door-lockmember coupled to the driven part.

2. Description of the Prior Art

The power conversion has conventionally been carried out by employing alink or a rack-and-pinion, etc., that is, the link converting mechanismor the rack-and-pinion converting mechanism has been conventionally usedfor the power conversion. In the aforementioned link conversionmechanism, the relationship of the thrust (F), the input torque (T), thepitch of a link arm (L), the stroke (S) and the rocking angle (θ) of thelink arm is represented by equations F=T/L and S=2 sin θ. Therefore, thestroke is 2L at the largest, and a large stroke can be obtained only atthe sacrifice of the thrust. On the other hand, in the case of therack-and-pinion converting mechanism, the relationship of the pitchradius (r) of a pinion, the thrust (F) and the input torque (T) isrepresented by an equation F=T/r, resulting in limit of the reduction ofspeed in relation to the minimum number of teeth of the gear.

Meanwhile, for solving the above-described disadvantages in the priorart and for determining the stroke and the scale of reduction in speedfreely to some extent, the use of a gear and a screw for the powerconversion is proposed in Japanese Patent Laid-open PublicationTokkaisho No. 61-261587 (261587/1986).

The above gear-and-screw mechanism is of such construction that a screw1 (a rotating shaft provided in an external thread) is interlocked withthe rotation of a motor 2 through gears 3 and 4, thereby to linearlymove an output member 5 screwed in the screw 1. Moreover, an output rod6 connected to a driver lever to be operated is detachably engaged withthe output member 5 by a clutch member 8 provided with a spring 7.Therefore, the above-described gear-and-screw mechanism is considerablycomplicated in the construction, with an increased number of partsrequired, resulting in high manufacturing cost and many assemblingtroubles.

SUMMARY OF THE INVENTION

An essential object of the present invention is to provide an electricactuator which is provided with an improved power converting mechanismemploying the combination of a gear and a screw, so that the scale ofspeed reduction and the stroke can be determined freely, realizingassembling readiness and reduction in manufacturing cost, etc., insimple construction with a reduced number of parts.

A further object of the present invention is to provide an electricactuator which is provided with an improved clutch device and which isarranged to securely transmit the rotary power of a motor and forciblystop the rotation of the motor when a member to be driven comes to astop point, thereby to avoid generation of unpleasant noised of themotor in simplified structure.

A still further object of the present invention is to provide anelectric actuator which is provided with an improved switch mechanism,so that the generation of chattering can be avoided, with securing thefull stroke of the door lock member, even when the switch mechanism ismounted with some errors, wherein it is so arranged that the stroke ofthe switch can be small while the door lock member has a large stroke,resulting in compact structure and saving of space.

Another object of the present invention is to provide an electricactuator in an electric door lock system inside a door of an automobilewhich is arranged to avoid intrusion of water inside the actuatorthrough a respiration hole, with securing the respiration operation,without any particular part therefore required.

In accomplishing the above-described objects, according to the presentinvention, a power converting mechanism is provided in an electricactuator which is comprised of a motor, a gear rotated by the motorthrough a centrifugal clutch, a final drive gear to be meshed with thegear, an internal thread formed in the inner peripheral surface of anaxial hole formed in the center of the final drive gear, a screw passingthrough the axial hole of the final drive gear to be supported thereby,and an external thread formed in the outer peripheral surface of thescrew. The external thread is screwed with the internal thread. On theother hand, there is formed a connection part at one end of the screw tobe connected to a driven member. Accordingly, the rotary power of themotor is converted to linear power of the driven member. In the casewhere the driven member is manually operated, the engagement of the gearwith the motor is released by the centrifugal clutch to stop therotation of the motor.

Moreover, a clutch device is provided in the electric actuator in whicha driver which is a rotating member at the input side and integrallyconstructed with an output shaft of the motor is provided with a weightin such a manner as to be immovable in a circumferential direction andmovable in a radial direction. Moreover, a convexed portion is formed inthe inner peripheral surface of a rotating drum which is loosely fittedin the driver and is a rotating member at the output side, so that theweight moving outwards in the radial direction by the centrifugal forceat the rotation of the motor is engaged with the convexed portion. Theengagement between the convexed portion and the weight transmits therotation of the motor to the rotating drum. When the rotating drum isstopped, the rotation of the driver is stopped, thereby restricting therotation of the motor.

Further, a switch mechanism is arranged in the electric actuator of thepresent invention. According to the arrangement, the stroke SA of anoutput member of the electric actuator is set larger than the stroke SLof the door lock member. At the same time, the distance of a pair ofarms protruding from the output member for engagement with a switchoperating tab is set to be larger than the width of the switch operatingtab, with forming a clearance. The switch operating tab is looselyfitted between the pair of the arms. During operation of the actuator,first, only the output member is moved by the distance (a). Then, theswitch operation tab is moved together with the output member. Thenecessary stroke SS,SSR for the switch is set smaller than the stroke SAof the output member, and at the same time, the stroke SS,SSR is setconsiderably smaller than the stroke SL of the door lock member toestablish SS,SSR<<SL<SA. Accordingly, the switch mechanism can becompact in size. Even when the mounting error is given rise to and thedoor lock member reaches the stroke end earlier, the output member isreversed owing to the stability of a mounting panel or a coupling rod,etc. elastically deformed by the operation of the electric actuatorafter interruption of power supply, but the switch operating tabremains. Therefore, chattering is prevented. Moreover, because of thearrangement that the stroke SA of the door lock member is made largerthan the stroke SL of the actuator, insufficient supply of power to theswitch never takes place. Accordingly, the door can be locked with thefull stroke of the door lock member and the door lock releasingoperation can be performed with certainty.

A skirt portion for enclosing a respiration hole is integrally formedwith a casing, or the skirt portion is integrally formed with a grommetwhen the respiration hole is formed in the portion where the grommet ismounted. Therefore, water drops running along the outer wall surface ofthe casing are arranged to flow tracing the outer wall surface of theskirt portion in the vicinity of the respiration hole, thereby toprevent the water drops from gathering in the respiration hole. Theintrusion of water into the casing as a result of the respiration canaccordingly be securely prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of the present invention willbecome clear from the following description taken in conjunction withthe preferred embodiments thereof with reference to the accompanyingdrawings, in which:

FIG. 1 is a plan view, partly cross-sectioned, of an electric actuatoraccording to the present invention, with an upper casing removed;

FIG. 2 is a cross sectional view taken along the line II--II of FIG. 1;

FIG. 3 is a cross sectional view taken along the line III--III of FIG.1;

FIG. 4 a perspective view of an essential portion of the electricactuator of FIG. 1 when it is exploded;

FIG. 5 is an exploded plan view of a contact mechanism of the electricactuator of FIG. 1;

FIG. 6, is a cross sectional view, on an enlarged scale, of a clutchmechanism employed in the electric actuator of FIG. 1;

FIG. 7 a perspective view of an essential portion of the clutch of FIG.6 when it is exploded;

FIG. 8 is a perspective view of a modification of FIG. 7;

FIG. 9 is a view schematically showing the structure of the electricactuator of FIG. 1 when it is installed in an automobile door;

FIG. 10 and FIG. 11 are views explanatory of the operationalrelationship between an output member and a switch operating tab of theelectric actuator of FIG. 9;

FIG. 12 is a timing chart in the case where a mounting error is broughtabout in the electric actuator of FIG. 9; and

FIGS. 13(A) and 13(B) are respectively a cross sectional view and abottom view of a part of a casing of the electric actuator of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

Before the description of the present invention proceeds, it is to benoted that like parts are designated by like reference numeralsthroughout the accompanying drawings.

With reference to FIG. 1, an electric actuator of the present inventionis so assembled that after a motor 2 and every part driven by the motor2 are mounted in a lower casing 11, and upper casing 10 is attached tothe lower casing 11. The electric actuator has the motor 2, acentrifugal clutch 3, a clutch device 4, a power converting mechanism 5,and a switch mechanism 6 accommodated in a casing 1. A lead wire 7 isguided outside the casing 1.

With regards to the centrifugal clutch 3, a clutch base 13 is pressed inan output shaft 12 of the motor 2 for fixing. The clutch base 13 hasprotruding pins 13a and 13a rotatably fitted in holes 14a and 14a formedin a pair of semi-circular clutch plates 14 and 14. Moreover, the clutchbase 13 is loosely fitted with a clutch bell 15 which is rotatablysupported by the output shaft 12. When the pair of the clutch plates 14and 14 are extended outwards in a radius direction at the fulcrum of thepins 13a and 13a by the centrifugal force upon rotation of the motor,the pair of the clutch plates 14 and 14 are pressed into contact withthe inner peripheral surface of the clutch bell 15 so as to transmit therotary power of the motor to the clutch bell 15.

With respect to the power converting mechanism 5, a gear 16 of a smalldiameter is integrally formed at one end of the clutch bell 15. A tooth16a formed in the outer peripheral surface of the gear 16 is meshed witha tooth 17a of a final drive gear 17 of a larger diameter arranged inparallel relation to the gear 16. The final drive gear 17 is fitted in adrum 24 through the clutch device 4. An axial hole is formed in acentral boss 24a of the drum 24, and an internal thread 24b is engravedin the inner peripheral surface of the axial hole. A screw 18 as a mainshaft is passed through the axial hole of the drum 24. The internalthread 24b is screwed and coupled with an external thread 18a protrudedin the outer peripheral surface of the screw 18. As shown in FIG. 1, theopposite sides of the screw 18 arc fitted in respective bearing portions11c and 11d of a partition wall 11a and an outer wall 11b in the lowercasing 11, so as to slidably support the bearings. Furthermore, thefinal drive gear 17 is rotatably fitted in a gap between the partitionwall 11a and the outer wall 11b in such a manner as to be immovable inan axial direction. Moreover, a stopper 18b in the shape of a squareplate standing at the terminal of the external thread 18a of the screw18 is fitted in a gap between guide portions 10a and 11e respectivelyprotrudingly formed in the casings 10 and 11 so as not to be rotatable.In this construction, it can be so arranged that the stroke of the screw18 is restricted when the stopper 18b comes into contact with theopposite end faces of the guide portions 10a and 11e. There is formed aconnecting portion 18c connected to the driven part (not shown) at theend of the stopper 18b to be integral with the stopper 18b. A connectinghole 18d is formed at the end of the connecting portion 18c.

When the motor 2 of the above-described electric actuator is driventhrough remote control, the clutch plates 14 and 14 are rotated throughthe base 13 in the centrifugal clutch 3 installed in the output shaft12. At this time, the pair of the clutch plates are pressed into contactwith the inner peripheral surface of the clutch bell 15 by thecentrifugal force. As a result of this, the rotary power of the motor 2is, through the output shaft 12, the clutch base 13, the clutch plates14 and 14, the clutch bell 15 and the gear 16, transmitted to the finaldrive gear 17 which is in turn rotated. Because of the rotation of thefinal drive gear 17, the drum 24 is rotated through the clutch device 4.Consequently, the internal thread 24b formed in the inner peripheralsurface of the axial hole of the central boss 24a is rotated. Since theinternal thread 24b is screwed in the external thread 18a of the screw18, the screw 18 is linearly moved. Accordingly, the connecting portion18d formed at one end of the screw 18 is linearly moved as shown by anarrow, thereby to automatically drive the interlocking door lock member.

In the manner as above, when the rotary power of the motor 2 isconverted to the linear power for the screw 18 which has the connectingportion to be connected to the driven member, the scale of the reductionin speed can be adjusted freely by the mesh of the gears 16 and 17, anda suitable large torque can be obtained. At the same time, by properlydetermining the angle of torsion of the external thread 18a of the screw18 and the internal thread 24b of the drum 24, the thrust can be setfreely within some range and moreover, by arranging the length of theguide portion 10a upon necessity, the stroke can be also set freely.

In the meantime, when supply of electricity is interrupted, thecentrifugal force of the pair of the clutch plates 14 and 14 is lost inthe centrifugal clutch. Therefore, the pressing force against the innerperipheral surface of the clutch bell 15 is scarcely remaining orcompletely lost. Thus, when the door lock member is manually operated,the screw 18 is moved, and consequently the gears 17 and 16 are rotated,but the motor 2 is not rotated by the centrifugal clutch, enabling easymanual operation from outside.

Further, in the case where the above-described electric actuator isinstalled in a keyless door lock mechanism, when the door is closedwithout an outer handle pulled out, the auto-unlock (self-cancellation)system is effected, resulting in abrupt operation of the actuator fromoutside. In the above embodiment, however, an armature of the motor 2and the clutch plates 14, etc. which have large inertial mass are shutoff by the centrifugal clutch 3 and the clutch device 4, andaccordingly, those parts are not moved at the operation from outside.Thus, the breakage of the interior of the actuator or the poor operationin self cancellation system can be avoided.

The present invention is not restricted to the above-describedembodiment. Although the motor 2 and the screw 18 are arranged inparallel relation in the aforementioned embodiment, it may be possibleby using a bevel gear that the motor 2 is arranged with right angleswith respect to the screw 18. Further, the clutch is not limited to theabove-described embodiment. A centrifugal clutch of a pinless(pivotless) type may be employed. If the centrifugal clutch of thepinless type is employed, the clutch plates fitted in the clutch baseare pressed into contact with the inner peripheral surface of the clutchbell by the centrifugal force, thereby to transmit the rotary power.Moreover, if the clutch plate of FIG. 1 is mounted with a return spring,light and easy manual operation from outside can be realized regardlessof the mounting position of the actuator.

The clutch device 4 will be described in more detail.

The clutch device 4 is comprised of the final drive gear 17 which is arotating member at the input side, a pair of weights 21 and 21, a spring22 and the rotating drum 24 which is a rotating member at the outputside. The final drive gear 17 has, as shown in FIG. 7, a disk part 25formed in the outer periphery at the lower end of an axial portionfitted in the main shaft of the screw 18. There are standing partitionwalls 26 and 26 separated 180° from one another on the disk part 25.Each partition wall 26 has a groove (not shown) notched in the outer endsurface thereof so as to be engaged with the spring. The weight 21 whichis centrifugally moved by the rotation of the motor is made of a heavymetal in the shape of a fan to be fitted with a fan-shaped storing space28 defined by the partition walls 26 and 26. Each of the weights 21 and21 is placed on the disk part 25 of the final drive gear 17 to beaccommodated in the corresponding storing space 28 in such a manner asto be unmovable in a circumferential direction and movable in a radialdirection. In the outer peripheral surface of the weight 21 is formed anengagement groove 29 to be engaged with the spring. The partly-notchedcircular spring 22 is engaged with the groove of the partition wall 26,and also with the engagement groove 29 of the weight 21, so that each ofthe weights 21 and 21 which projects by its centrifugal operation can beaccommodated in the storing space 28 when the motor 2 is stopped. Therotary drum 24 is formed with the internal thread 24b in the axial holeof the central boss 24a outfitted in the screw 18. The boss is rotatablybutted against the external thread 18a in the axial part of the finaldrive gear 17. The rotating drum 24 is further provided with acylindrical part 30 in the outer periphery thereof, which cylindricalpart 30 is rotatably fitted inside the final drive gear 17. The innerperipheral surface of the cylindrical part 30 is defined alternately tobe a large diameter portion and a small diameter portion separated 180°from each other. In other words, a pair of recessed portions 30a and 30aare defined in the large diameter portion and a pair of convexedportions 30b and 30b are formed in the small diameter portion. A steppedface 31 is formed between the recessed portion 30a and the convexedportion 30b in a radial direction for engagement with the weight.

In the clutch device having the above-described construction, since theweight 21 is normally urged by the spring 22 in the cylindrical part 30of the rotating drum 24, the weight 21 is not in touch with the innerperipheral surface of the convexed portion 30b, nor is it connected tothe rotating drum 24. When the motor 2 is driven by remote control, thefinal drive gear 17 is accordingly rotated, and also the weight 21 andthe spring 22 accommodated in the final drive gear 17 are rotated.Consequent to the rotation, the weight 21 is pushed outwards by thecentrifugal force in a radius direction against the spring 22. Then theweight 21 is fitted in the recessed portion 30a of the rotating drum 24,with the one end face of the weight 21 being engaged with the steppedsurface 31. Therefore, the rotary power of the motor 2 is transmitted tothe rotating drum 24, thereby rotating the final drive gear 17, theweight 21 and the rotating drum 24 all together. At this time, even ifthe motor 2 is burdened with some load, and the rotation of the motor 2is deteriorated, the rotary power of the motor 2 is securely transmittedto the rotating drum 24 so long as the weight 21 is engaged with thestepped face 31.

When the electricity is stopped being supplied to the motor 2, theweight 21 is depressed towards the central direction by the repulsion ofthe spring 22. As a result, the weight 21 is accommodated in the storingspace 28 of the final drive gear 17 and returned to the state where theengagement with the rotating drum 24 is released. While the supply ofthe electric power to the motor 2 is stopped, the driven members afterthe rotating drum 24 are in the free state. Therefore, when the doorlock operation is manually carried out to drive the lever, only thefinal drive gear 17 is idly rotated, and the motor 2 is never rotated.Accordingly, the door lock operation can be easily performed throughmanual operation with no large force required.

FIG. 8 shows a modified embodiment of the clutch device. The weight ofthe modified device is of a pivot type. The pair of the weights 21 and21 are formed in semi-circular shape, at the one end of each of which isformed a fitting aperture 21a for a pin 33 and at the other end of eachof which is formed an engagement hole 21b for the spring 22. The finaldrive gear 17 has two pins 33, instead of the partition walls 26,provided adjoining the disk part 25. Each pin 33 is fitted in the pinfitting aperture 21a of the weight 21. The weights 21 are rotatablyarranged in a circular configuration around the pins 33. In addition,the spring 22 is mounted in the outer peripheral surface of the weight21. Bending portions 22a and 22b at the opposite ends of the spring 22are inserted in and engaged with the engagement holes 21b of the weight21, so that the front ends of the weights 21 are urged by the spring 22to approach each other. In this modified embodiment, when the finaldrive gear 17 is rotated consequent to the rotation of the motor, thefront ends of the weights 21 are extended outwards by the centrifugalforce against the force of the spring 22, and the front end of eachweight is brought in engagement with the convexed stepped face 31 of therotating drum 24. Thus, the rotation of the motor is transmitted to therotating drum 24. When the electric power supply to the motor 2 isinterrupted, the weights 21 are so urged by the spring 22 as to comecloser to each other, thereby cutting the engagement of the weights tothe rotating drum 24. The modified embodiment described above isaccordingly advantageous in simplified structure of the final drive gear17.

Next, the switch mechanism of the electric actuator will be describedhereinbelow in more detail.

Referring t FIG. 9, the electric actuator is installed inside a door 40.A coupling rod 42 is connected to one end of an output member 50 havingan internal thread 50a and provided at the front end of the screw 18. Atthe other end of the coupling rod 42 is connected a door lock member 43of the driven member. In the case where the door lock member 43 isautomatically operated, and when the motor of the electric actuator inthe door 40 is supplied with electricity through remote control from adriver's seat, the final drive gear 17 is rotated. Then, one end of theoutput member 50 of the screw 18 which is meshed with the final drivegear 17 through the power converting mechanism and the clutch device islinearly moved. Corresponding to the movement of the output member 50,the door lock member 43 is driven through the coupling rod 42 so as toautomatically lock or unlock the door 40.

Arms 45 and 46 for engagement with a switch operating tab 49 areprotrudingly provided at the opposite ends of the output member 50. Arecess 47 is formed between the arms 45 and 46 which are confrontingeach other. The operating tab 49 of a limit switch 48 is loosely fittedin the recessed portion 47. In this case, the distance between the arms45 and 46 is set to be larger than the width of the operating tab 49 bythe distance (a), namely, the clearance (a). Because there is providedthe clearance (a), the moving stroke of the switch operating tab 49 isset smaller than the stroke of the output member 50 by the clearance(a). In the limit switch 48, when the operating tab 49 comes to aposition (P,P') separated a little with respect to the stroke end at theopposite ends of the guide portions 10a and 11d in the switch casing, itis the position to be detected when the supply of electricity to themotor 2 should be interrupted. The charging stroke of the limit switch48 SS,SSR is set to be considerably smaller than the stroke SL of thedoor lock member 43. Therefore, the relationship of the door lock strokeSL, the actuator (output member) stroke SA and the switch chargingstroke SS,SSR is determined as follows.

    SS,SSR<<SL<SA

The operation of the above-described switch mechanism will be explained.

When the motor 2 is supplied with electricity and the final drive gear17 is rotated in a direction shown by an arrow, the output member 50 islinearly moved in the direction shown by the arrow. In this case, asshown in FIG. 10, the operating tab 49 is, in the beginning, in pressedcontact with the arm 45, with the distance (a) separated from the arm46, and accordingly only the output member 50 is moved while theoperating tab 49 is left behind. After the output member 50 is moved (a)distance, the arm 46 is contacted with the operating tab 49. Inconsequence, the output member 50, together with the operating tab 49,is moved. When the operating tab 49 is moved a predetermined distance toreach the position P, the supply of electricity to the motor 2 isinterrupted. Similarly, when the motor 2 is reversed and both the outputmember 50 and the operating tab 49 are moved in an opposite direction,since the operating tab 49 is at first in contact with the arm 46, withthe distance (a) kept from the arm 45, as shown in FIG. 11, only theoutput member 50 is moved. Thereafter, when the output member 50 ismoved the distance (a), the arm 45 is brought in contact with theoperating tab 49, so that the output member 50 is moved integrally withthe operating tab 49. When the output member 50 comes to the positionP', the supply of electricity is interrupted. Thus, in the manner asabove, when the output member 50 is moved, first, only the output member50 is moved and the operating tab 49 is left behind. Then, after theoutput member 50 is moved a predetermined distance (the distance (a)),the operating tab 49 is moved together with the output member 50.Therefore, the stroke of the operating tab 49 can be rendered small.

Even if the door lock member 43 is positioned with some error or thelength of the coupling rod 42 is erroneously set, since the stroke SL ofthe door lock member 43 is set larger than the stroke SA of the outputmember 50 as indicated in a timing chart of FIG. 12, the output member50 and the operating tab 49 are arranged to reach the terminal point ofthe stroke earlier than the door lock member 43, to stop the supply ofelectricity, thereby to avoid such accident that the door lock member 43can not be moved with full stroke. Moreover, contrary to the above, evenwhen the door lock member 43 comes earlier to the end of the stroke,after the interruption of the power supply, the output member 50 isreversed and moved in the opposite direction by the stability of themounting panel, the coupling rod, etc. which are elastically deformedbecause of the operation power of the electric actuator, but the outputmember 50 starts moving with the operating tab 49 remaining in thebeginning. Therefore, chattering is never brought about.

In the embodiment shown in FIG. 1, a skirt portion 54 is protrudeddownwards from the outer periphery of a respiration hole 53 opened atthe bottom of the casing 1. The skirt portion 54 is integrally formedwith the casing 1. As indicated in FIGS. 13(A) and 13(B), the skirtportion 54 is so arranged that the inner peripheral surface 54a thereofis positioned as far as possible from the respiration hole 53. At thesame time, the sectional area and the configuration of the skirt portion54 are so designed as not to gather water thereat by the surface tensionand the capillary action. The cross section of the skirt portion 54 isoval as shown in FIG. 13(B) according to the present embodiment, but itmay be polygonal.

Owing to the above-described construction, the water running along theouter wall surface of the casing 1 falls down along the outer peripheralsurface 54b of the skirt portion 54. Simultaneously, even if the water Wrises along the inner peripheral surface 54a of the skirt portion 54 bythe capillary phenomenon, since the skirt portion 54 is kept away fromthe respiration hole 53, the water does not fall in the respiration hole53. Accordingly, it can be prevented that the water gathers at theopening mouth of the respiration hole 53, and the water invades into therespiration hole 53. Therefore, in the case where a bellows 56 isprovided between the upper end of the casing 1 and the driven lever 55,the water can be surely prevented from entering the casing 1 through therespiration hole 53 even by the respiration of the actuator.

As a modification of the present invention, the respiration hole may beformed in a grommet for guiding the lead wire. In this case, a protrudedpart is formed at the bottom of the casing 50 so as to be fitted in withthe grommet. The respiration hole is formed in the center of theprotruded part, and a guide hole for introducing the lead wire is formedat a position separated from the respiration hole.

Meanwhile, the grommet to be fitted in the protruded part has anH-shaped cross section. The upper half of the grommet is outfitted inthe protruded part, from which the skirt portion is projected. Arespiration hole is formed in the center of the lateral cross section ofthe grommet fitted in the bottom surface of the protruded part, with aguide hole for the lead wire formed away from the respiration hole. Thelead wire for supply of electricity and for transmission of signals isinserted from the guide hole of the grommet through the guide hole inthe protruded part into the casing 50.

According to the modified embodiment also, the water drops flowing alongthe outer peripheral surface of the grommet from the outer wall surfaceof the casing 50 are guided down along the skirt portion, thereby toprevent gathering of the water drops in the respiration hole away fromthe skirt portion. Therefore, it is advantageous that the water drops donot intrude inside the casing 50 from the respiration hole in theprotruded part through the respiration hole of the casing.

As has been described hereinabove, the power converting mechanismprovided in the electric actuator of the present inventionadvantageously makes it possible to freely set the scale of the speedreduction and the stroke, and to reduce the number of parts remarkablyas compared with the prior art. Specifically, the connecting portion tobe connected with the driven member is integrally formed with the screwengaged with the final drive gear, and moreover the screw is supportedby the bearing portion integrally formed with the casing. The finaldrive gear is supported by the screw. Accordingly, no special componentis necessary for the rotating bearing of the final drive gear, resultingin considerable reduction of the number of component parts.Consequently, the cost of parts is reduced, and assembling operation canbe conducted with much ease.

Furthermore, according to the clutch device of the electric actuator ofthe present invention, the driver integrally formed with an output shaftof the motor is provided with a pair of weights in such a manner thatthe weights can not be moved in a circumferential direction. 0n theother hand, a convexed portion is formed in the inner peripheral surfaceof the rotating drum at the output side which is loosely fitted in thedriver, so that the weight moving outwards in a radial direction by thecentrifugal force at the rotation of the motor is engaged with theconvexed portion. Accordingly, the rotary power of the motor istransmitted to the rotating drum owing to the engagement of the weightwith the convexed portion. Moreover, when the rotating drum is stopped,the rotation of the driver is stopped, restricting the rotation of themotor. Thus, when the operating member interlocking with at the side ofthe rotating drum, for example, the door lock member reaches apredetermined position to be stopped, consequently stopping the rotatingdrum, the weight of the clutch device is idly rotated, and thereforeunpleasant noises can be prevented from being generated between therotating drum and the clutch device. Moreover, when the operating memberis driven by the motor through the clutch device, the rotating power ofthe motor is transmitted because of the engagement of the weight movingoutwards by the centrifugal force with the convexed portion formed inthe inner peripheral surface of the rotating drum. As a result, evenwhen the rotation of the motor is deteriorated, the engagement is nevereasily released, with ensuring safe transmission of the rotation of themotor to the rotating drum at the output side. Therefore, it isadvantageous that the capacity of the motor can be utilized to themaximum, resulting in compact structure of the motor, according to theclutch device of the electric actuator of the present invention.

Since the switch charging stroke is set considerably smaller than thedoor lock stroke in the witch mechanism of the electric actuator of thepresent invention, the switch can be rendered compact in size, savingspace, even in the case where the door lock stroke is large. Incomparison with the prior art, the switch mechanism is so simple instructure that the operating tab of the switch can be engaged with thearms if only a pair of arms projecting from the output member areextended, resulting in low manufacturing cost. In addition, chatteringcan be advantageously avoided even when the switch mechanism is mountedwith some errors. Moreover, even insufficient supply of electricity tothe switch does not hinder the door lock member to move with fullstroke. Accordingly, owing to the switch mechanism of the electricactuator of the present invention, the door lock member is able to beautomatically operated with certainty.

The skirt portion is integrally formed with the casing so as to enclosethe respiration hole formed in the bottom of the casing, or the skirtportion is integrally formed with the grommet in the case where therespiration hole is formed in the grommet. Accordingly, the water dropsfalling down the outer wall surface of the casing are arranged to flowalong the outer wall surface of the skirt portion. Thus, the gatheringof water drops in the opening mouth portion of the respiration hole canbe prevented and, if the water do gather, they are sucked into thecasing by the respiration of the bellows. Moreover, since the skirtportion is formed integrally with the casing or grommet, withoutrequiring any particular part other than in the prior art, in order tofulfill the objects of the present invention, the increase of themanufacturing cost can be avoided. Moreover, such lengthy pipe is notemployed in the present electric actuator as in the prior art, and therespiration hole is opened within the skirt portion, so that normalrespiration is assured at all times.

Although the present invention has been fully described in connectionwith the preferred embodiments thereof with reference to theaccompanying drawings, it is to be noted that various changes andmodifications are apparent to those skilled in the art. Such changes andmodifications are to be understood as included within the scope of thepresent invention as defined by the appended claims unless they departtherefrom.

What is claimed is:
 1. An electric actuator provided with a powerconverting mechanism which comprises:a motor provided with an outputshaft; a centrifugal clutch including a centrifugal clutch drivingsection connected to the output shaft, and a centrifugal clutch drivensection having an internal peripheral surface concentric with saiddriving section and connectable with said driving section undercentrifugal force; a gear which is integral with said driven sectionsand rotatably supported on the output shaft of said motor; a final drivegear meshing with said gear, a drum member concentric with said finaldrive gear and provided with a boss portion having an internal threadformed in an inner peripheral surface of a central axial opening;centrifugally actuated clutch means provided between said final drivegear and said drum member; a screw passing through the axial opening ofsaid boss portion and having an external thread formed on an outerperipheral surface thereof, so that the external thread is threadlyengaged with said internal thread; and a connecting portion at one endof said screw, connected to a driven member, whereby rotary movement ofsaid motor is converted into linear movement of said driven member.